1. Field of the Invention
The invention relates in general to a vibration damper, and more particularly to a vibration damper on which a scanner can be mounted.
2. Description of the Related Art
New methods for achieving high resolution of photolithography are continually developed to manufacture devices with higher precision, as semiconductor are increasingly integrated. In the future, scanners are expected to become mainstream technology because of the requirements of 0.18 .mu.m size devices. Therefore, the dampening ability of the vibration damper has to increase as well. The required vibration damper prevents floor vibrations from disturbing the scanner and avoids the force produced by the scanner, which the scanner can't disperse and which may affected the next exposure step of the scanner.
Semiconductor manufactory floors are metal grids or have holes in them to to facilitate the connections of several kinds of culverts in the manufactories. Therefore, these floors are less dense than solid, flat floors. When a scanner is mounted on such a floor, it is necessary that the vibration damper be light, since the scanner itself already weighs about 7200 kg.
The conventional vibration damper is a steel baseplate with a simple structure that has a poor damping ability. Therefore, the conventional vibration damper is only suitable for processes with low precision requirements and is not suitable for devices with sizes less than 0.1 .mu.m because of its poor damping ability. The improved vibration damper is composed of ferroconcrete so that the vibration-proof ability is improved. However, this type of vibration damper is at least 2000 kg heavier than the scanner, and the floors of the manufactories cannot bear that much weight. Therefore, the conventional vibration damper does not meet the actual requirements of the processes. A need exists for an improved damper.